I'm having the same issue. I tried running the game as admin but the issue persists. I tried creating an Autosave.raf at that location, but that didn't do anything either. Is there anyway I can disable autosave for now? Any other ideas for things to try?

I have the game in Steam and I rolled back to v1.4 and now everything is working fine. For anyone else with this issue, go to the game in your library, right click and choose properties. Go to the Betas tab and you'll see a dropdown to select the beta you would like to opt into. One of the options is legacy - version 1.4. Select that and steam will then 'update' the game. In your library, you will see that it now says Reus [Legacy]. You should be good to go now, at least as far this autosave issue goes.